1. Field of the Invention
This invention relates to a method of manufacturing a pneumatic tire wherein a carcass ply is divided in a central portion of a tread as well as a pneumatic tire manufactured by this method.
2. Description of Related Art
Recently, a frequency of running a vehicle at a high speed becomes higher together with the servicing of express ways and so on, and hence pneumatic tires are is demanded to indicate a low road noise. As a pneumatic tire capable of running at a low road noise, JP-A-11-11109 proposes a pneumatic tire wherein a carcass ply is divided in a central portion of a tread at a state of removing a central portion of the carcass ply to give a flexibility to the tread portion. Such a tire is very advantageous to improve both steering stability and ride comfort against vibrations.
If it is intended to manufacture such a pneumatic tire by the well-known method, as shown in FIG. 5, an innerliner 18 is first wound on a central zone of a first cylindrical shaping drum 11 and wire chafer 15 is wound on each side zone thereof, and thereafter a pair of side carcass layers 14 are wound on the outsides of the innerliner and wire chafer so as not to locate them on a center of the first shaping drum. Then, the central zone of the first shaping drum is somewhat enlarged to form a step difference in the side carcass layer and further a bead core 13 provided with a filler is set on the outside of the step difference of the side carcass layer. Next, a folded bladder 12 of the first shaping drum 11 is expanded to turn up the side carcass layer 14 and wire chafer 15 located outward from the bead core 13 around the bead core 13. Then, a rubber chafer and a sidewall rubber previously joined to each other are wound on an outer circumference of a turnup portion of the side carcass layer to form a green case 16.
After the thus formed green case 16 is transported onto a second shaping drum 19, as shown in FIG. 6, a shaping bladder 17 is expanded in the green case 16 while approaching the bead cores 13 to each other, whereby the green case 16 is shaped into an approximately semi-circular form at its section. Thereafter, a cylindrical belt-tread band formed in another band shaping drum is supplied to the circumference of the green case 16 and laid thereon to form a green tire.
However, when the green case 16 is deformed into the approximately semi-circular form at its section by the shaping bladder 17 of the second shaping drum 19, since only the innerliner 18 having a very low stiffness is existent between top ends 14a of the side carcass layers 14, the innerliner 18 is stretched therebetween to make the thickness thereof thin. As a result, there are problems that air leakage is caused in a tire product and tire uniformity lowers. And also, the position of the top end 14a of the side carcass layer 17 becomes unstable due to the stretching of the innerliner 18, which further degrades the tire uniformity.
It is, therefore, an object of the invention to solve the above problems of the conventional technique and to provide a method of manufacturing a pneumatic tire which can improve the tire uniformity while preventing the occurrence of air leakage as well as pneumatic tires manufactured by this method.
According to a first aspect of the invention, there is the provision of a method of manufacturing a pneumatic tire, comprising the steps of:
a step of laying a central innerliner on an outer circumference of a shaping drum with an outer surface form being approximately the same as an inner surface form of a tire product;
step of laying an approximately ring-shaped sidewall assembly comprising a bead core provided with a bead filler, a side carcass layer folded so as to envelop a circumference of the bead core provided with the bead filler and an outside innerliner laid on an innermost side of the side carcass layer on each side face of the shaping drum;
a step of laying a belt comprised of plural belt layers on the circumference of the central innerliner and sandwiching a top end of the outside innerliner and an inside top end of the side carcass layer between side end portions of the belt and the central innerliner; and
a step of laying a tread rubber on the circumference of the belt.
According to a second aspect of the invention, there is the provision of a method of manufacturing a pneumatic tire, comprising the steps of:
a step of laying a central innerliner on an outer circumference of a shaping drum with an outer surface form being approximately the same as an inner surface form of a tire product;
a step of laying a part of plural belt layers constituting a belt on the circumference of the central innerliner;
a step of laying an approximately ring-shaped sidewall assembly comprising a bead core provided with a bead filler, a side carcass layer folded so as to envelop a circumference of the bead core provided with the bead filler and an outside innerliner laid on an innermost side of the side carcass layer on each side face of the shaping drum;
a step of laying the remaining belt layer on the circumference of the belt layer and sandwiching a top end of the outside innerliner and an inside top end of the side carcass layer between side end portions of the precedently laid belt layer and subsequently laid belt layer; and
a step of laying a tread rubber on the circumference of the belt.
As mentioned above, in the manufacture of the pneumatic tire according to the invention, the central innerliner, belt layers and tread rubber are laid on the outer circumference of the shaping drum having an outer surface form being approximately the same as an inner surface form of a tire product, and the sidewall assembly of approximately the ring-shaped form having the bead core provided with the bead filler, the side carcass layer and the outside innerliner is laid on each side face of the shaping drum, so that a step of expanding and deforming the green case into approximately the semi-circular form is removed and hence the innerliner is not locally stretched. Thus, the occurrence of air leakage in the tire product can be prevented and also the tire uniformity can be improved because the position of the top end of the side carcass layer is stabilized.
Particularly, when the top end of the outside innerliner and the inside top end of the side carcass layer are sandwiched between the side end portions of the belt layers, the position of the top end of the side carcass layer is can further be stabilized and a certain internal tension can be applied to the side carcass layer, whereby the tire uniformity can be more improved.
In a preferable embodiment of the invention, the sidewall assembly further comprises a cord-reinforced chafer laid on the circumference of the side carcass layer so as to envelop the bead core and a sidewall rubber laid on the circumference of the side carcass layer outward from a top end side of the chafer.